An isothermal process is a thermodynamic process in which a system's temperature is held constant, typically by placing it in thermal contact with an infinitely large reservoir that supplies or absorbs heat as needed. Because temperature is constant, internal energy (proportional to average kinetic energy) does not change, so by the first law of thermodynamics (ΔU = Q − W) the heat added to the system equals the work done by the system (Q = W). For an ideal gas following PV = nRT, holding T constant means pressure and volume are inversely related (P = k/V), tracing a rectangular hyperbola called an isotherm on a PV diagram, and the work done during the process is found by integrating P dV, yielding W = nRT·ln(V2/V1).
An isothermal process is a thermodynamic process in which a system's temperature is held constant, typically by placing it in thermal contact with an infinitely large reservoir that supplies or absor…